1. Field of the Invention
This invention relates to amphoteric water-in-oil self-inverting polymer emulsions for use in papermaking, sewage treatment, drilling muds and petroleum recovery by water flooding.
2. Description of the Prior Art
Water-in-oil self-inverting polymer emulsions are used in commercial applications such as papermaking operations, treatment of sewage and industrial wastes, drilling muds, secondary and tertiary recovery of petroleum by water flooding.
Three types of polymeric emulsions, i.e., nonionic, cationic and anionic emulsions are known. Preparation of these emulsions is described in numerous patents. The internal phase of the emulsion is formed from a water solution of an ethylenic unsaturated monomer or comonomer such as (1) acrylamide, methacrylamide, (2) acrylic acid, methacrylic acid, (3) dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethyl and diethylaminoethyl acrylate, allyl methacrylate and its quaternization products, (4) N-substituted methacrylamide and (5) vinyl sulfonate.
The external phase of the emulsion is formed using low HLB emulsifiers such as mono and diglycerides of fatty acids, sorbitan fatty acid monoesters, polyoxyethylene alcohols and the like dissolved in a solvent such as kerosene, xylene, toluene and chlorinated hydrocarbons.
A water-in-oil emulsion is produced by slowly adding the water phase to the oil phase under rapid agitation. The emulsion is homogenized to obtain the proper particle size and is then polymerized by one of the procedures described in the literature. After polymerization is completed, the final step is the incorporation of an inverting agent, a high HLB surfactant, into the emulsion. The finished emulsion is uniform and disperses instantly by self-inversion in a water system. Water-in-oil emulsions and their uses have been described in the prior art. The following patents are representative of the prior art.
U.S. Pat. No. 3,284,393 - Vanderhoff et al., issued Nov. 8, 1966, describes polymerization of vinyl monomer in the oil phase by forming a water-in-oil emulsion of the monomer in a hydrophobic liquid and water with a water-in-oil emulsifier and then polymerizing the emulsion with a free radical catalyst to obtain a polymeric latex where the oil phase is the dispersion medium.
U.S. Pat. No. 4,022,731 - Schmitt, issued May 10, 1977, describes a self-inverting water-in-oil emulsion containing an acrylamide polymer in the aqueous phase, hydrocarbon oil, water-in-oil emulsifier and an inverting surfactant mixture containing two sulfosuccinates or one sulfosuccinate and an alkylphenol ethoxylate.
U.S. Pat. No. 4,022,736 - Schmitt, issued May 10, 1977, describes a self-inverting water-in-oil emulsion having a copolymer of acrylic acid in the aqueous phase, hydrocarbon oil, water-in-oil emulsifier and an inverting surfactant which is a fatty alcohol ethoxylate.
U.S. Pat. No. 4,077,930 - Lim et al., issued Mar. 7, 1978, describes a stable, self-inverting water-in-oil emulsion obtained by emulsifying water soluble vinyl monomer in oil containing at least 20% emulsifier and a free radical catalyst and then polymerizing to obtain a stable polymer emulsion which can be inverted by adding water without any other reagent.
A common practice in plant operations such as in a paper mill is to change the charge in the system by switching from a nonionic polymer emulsion to a cationic or anionic polymer emulsion. In paper mill operations, the zeta potential should be determined to obtain optimum results. Choice of polymer emulsion depends on the type of charge in the previous operation and the type of charge required in the present operation. A change in charge is cumbersome and may require addition of varying quantities of a variety of polymers having different positive or negative charges.